Update 1/2/2014 - I updated the files to include a couple of improvements.
First, I added a parameter to control the spacing between the fingers. This allowed me to make the hand slightly narrower to suit the person for whom it is being made.
Second, and probably more importantly, I included parameters that allow the use of standard button head screws rather than specialized, long bolts or threaded rods. The first (and preferred) option is to place nut traps in the inside of the end slots. The traps are deep enough to hold M4 jam nuts. You can then use two standard button head screws of about half the needed width. They will thread through the nuts to lock tightly into place. If the hand is too small to accommodate the jam nuts, then I also included options for smaller size holes on the ends. Those holes could be tapped for M4 thread so that the entire first portion of the knuckle block serves as the trapped nut. If you use that, however, be careful not to over tighten the screws.
I am using this version on my latest test builds with 40mm M4 button head screws through each end and locking into place via the captive M4 jam nuts. It is working very well. The screws are solidly in place, but are not interfering at all with the mobility of the fingers.
This is a parametric version of the knuckle block used for Robohand.
This part goes with the Proximal and Distal Phalanges that I have published. The main benefit to this part is the ability to set the size of the holes. That allows you to use different size rod for the knuckle bolt (like if you are in the US and have only limited access to metric sized hardware). Of course, you could just use the stock part and drill out the hole you need - unless you need a smaller hole. You can also adjust the size of the slots to better fit the proximal parts. There is a support option to make it a bit easier to get a good print.
I have made a first test print of this. This is really not very different from the stock part - just slightly more configurable. It appears to work properly, but the hand is not complete and more testing is needed. For that reason, I am going to call this a work in progress for now.
NOTE: I have no medical training whatsoever, and make no warrantee of any sort regarding this part. I am providing it in the hopes that it will be helpful for others. If, however, you intend to use it, seek appropriate medical attention from a trained physician.